Infant colic or prolonged, inconsolable crying in an otherwise healthy infant has been a source of confusion for parents and pediatricians alike. Much of this confusion is due to the inconsistent criteria by which colic is identified and the lack of concrete evidence as to its origins. In addition, a small number of studies have revealed that colic may influence later infant behavior. The purpose of the proposed research is to address these issues by investigating the physiological and behavioral antecedents and correlates of infant colic and to examine the impact of colic on later behavior. Toward these ends, this research proposes to prospectively study a group of colic and non- colic infants from birth to five months of age. The emergence of colic will be identified at its onset and behaviors associated with colic obtained through the use of health diaries. Physiological activity during baseline and colic conditions will also be recorded. At five months of age, infant reactivity and responsivity will be measured through laboratory procedures and parental ratings of temperament. The results of this study will provide important information for the design and implementation of a large scale longitudinal study of the development and impact of colic.